1. Technical Field
The present disclosure relates to workpiece conveying apparatuses for conveying a number of workpieces such as chip electronic components, and more particularly to workpiece conveying apparatuses and electronic-component conveying apparatuses that convey workpieces by moving on a conveying stage a conveying table having through holes serving as holders in which workpieces are held.
2. Background Art
Conventionally, in manufacturing chip electronic components, after chip electronic components are fabricated, their properties are inspected, and, in accordance with the properties, the chip electronic components are sorted into non-defective and defective products. In some cases, the manufactured chip electronic components are classified into a plurality of groups in accordance with their properties. To automate such operations for higher productivity, various manufacturing apparatuses have been proposed.
For example, Patent Document 1 below discloses an example of such electronic-component conveying apparatuses. The electronic-component conveying apparatus includes a disc-shaped conveying table disposed on and in contact with a conveying surface of a table base so as to convey electronic components. The disc-shaped conveying table is connected to a rotary drive source in such a manner as to be rotatable about its central axis. The conveying table has along its circumferential direction a plurality of through holes each receiving one of the electronic components that are fed in sequence from a hopper. The electronic components are fed from the hopper into the respective through holes. When the conveying table rotates while sliding on the conveying surface of the table base, the electronic components are conveyed in the circumferential direction.
In this case, while the electronic components are conveyed in the circumferential direction, properties of the electronic components are measured. In accordance with the results of the measurement, the electronic components that have been subjected to the property measurement are dismounted from the through holes by arbitrary electronic-component dismounting means so as to be sorted into non-defective and defective products or classified according to the measured properties.
To maintain the position of the electronic components during the conveyance, the conveying surface is provided with vacuum recesses communicating with the through holes, and the vacuum recesses are connected to a vacuum source.
On the other hand, to dismounting the electronic components that have been subjected to the property measurement, a structure shown in FIG. 4 is used. As shown in FIG. 4, in an electronic-component conveying apparatus 101, the conveying table 102 has through holes 102a. Electronic components 104 are held in the through holes 102a. One surface 102b of the conveying table 102 is in contact with a conveying surface 103a of a table base 103.
In the conveying surface 103a of the table base 103, blowholes 103b open at positions at which the electronic components 104 are to be dismounted. The blowholes 103b extend from the conveying surface 103a through to a surface 103c, which is the surface opposite the conveying surface 103a, and is connected to a compressed-air supply hose 105. The compressed-air supply hose 105 is connected to a compressed-air supply source, such as a compressor or a gas cylinder.
When the electronic component 104 after the measurement is brought to the electronic-component dismounting position, the blowhole 103b having smaller diameter than that of the through hole 102a is beneath the through hole 102a. Then compressed air is blown through the blowhole 103b. The pressure of the compressed air moves the electronic component 104 to outside the through hole 102a. Thus, the electronic component 104 is dismounted.
In this method, since the electronic components 104 can be dismounted without receiving mechanical impact, the electronic components 104 are negligibly damaged.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-226101
As described above, the conveying table 102 moves independently from the table base 103 while sliding on the conveying surface 103a of the table base 103. Therefore, after the electronic component 104 is dismounted by using the compressed air, the conveying table 102 is further rotated. Consequently, the blowhole 103b is closed again by the surface 102b of the conveying table 102.
In this case, there will be no problems if the compressed air is completely released toward the through hole 102a when the electronic component 104 is dismounted, and subsequently the blowhole 103b is closed by the surface 102b of the conveying table 102 after the supply of the compressed air is stopped.
In some cases, however, if the conveying speed is increased, the opening of the blowhole 103b is closed by the conveying table 102 with some compressed air remaining inside the blowhole 103b. In such a case, the compressed air remaining inside the blowhole 103b acts as a residual pressure.
Thus, in some cases, when the conveying table 102 is further rotated and an adjacent through hole holding another electronic component therein that is not to be dismounted at the electronic-component dismounting position is positioned over the blowhole 103b, the electronic component that is not to be dismounted is sometimes dismounted because of the residual pressure. Therefore, in the conventional electronic-component conveying apparatus, the conveying table 102 needs to be stopped for a predetermined time period after the electronic component 104 is dismounted, without being rotated immediately, so that the air is completely released. That is, a waiting time is necessary for releasing the residual pressure, which prevents such an electronic-component conveying apparatus from being operated at a high speed.
Particularly, as the size of the electronic components becomes smaller, the size of the blowhole 103b also needs to be smaller. Since a smaller blowhole 103b cannot blow a sufficient volume of air, the waiting time for eliminating the residual pressure needs to be further increased. There is another problem that, even if the waiting time is increased, it is still difficult to sufficiently release the residual pressure.